1. Technical Field
The present invention generally relates to fluid flow metering and control devices, and more particularly relates to flow blender devices for metering and controlling multiple fluid flows.
2. Related Art
There is a wide variety of production processes that require the blending or mixing of two or more fluids to form a “blended fluid”. Some examples of this are the production of paints and fragrances, where a base fluid is blended with highly concentrated color or fragrance fluids. Another example is chemical processing, where de-ionized water can be mixed with a concentrated chemical to create the correct dilution of the chemical for an upcoming production process. FIG. 16 shows a block diagram of a system which combines or blends three fluids into one fluid. The system of FIG. 16 includes fluid inputs I1-3, valves V1-3, and flow meters FM1-3. The resulting output O1 of the system shown in FIG. 16 is a blended fluid.
Users will often build fluid blending systems using discrete components such as those shown in FIG. 16. The blending ratios are typically controlled by individually adjusting the valves V1-3 to get the correct flow rates through each of the flow meters FM1-3. In a more automated system, a host computer monitors the output of the flow meters FM1-3 and adjust the valves V1-3 to get the desired flow rates for each fluid, and hence the desired blend in the output O1. The computer monitors the flow meters Fm1-3 via an analog output signal such as 4-20 mA, or via a digital communications signal such as a CAN bus signal using a protocol such as DeviceNet. The computer controls the valve openings via an electric or pneumatic control signal.
FIG. 17 shows another block diagram of an example control system for the fluid blending device shown in FIG. 16. In the system of FIG. 17, flow controllers C1-3 each include one of the control valves V1-3, flow meters FM1-3, and a control algorithm. The flow set points Fsp1-3 for each of the flow controllers can be received by the controllers C1-3 via an analog, digital or manual input signal. If the system is automated, the set points Fsp1-3 can be provided by a host computer. The percentage volume of each of the fluids in the final fluid is controlled by individually adjusting the flow rates of each valve and flow meter using the individual controllers C1-3. If the total flow rate needs to be adjusted and the blend kept the same, each flow controller must have its set point changed by the same percentage.
Users commonly build their own customized fluid blending systems using discrete components such as those shown in FIG. 16. Building such a fluid blending system typically requires the user to study, identify, procure, and maintain spare parts for the correct valves and flow meters for the system. The blending ratio and total flow rate for the system may be controlled by manually adjusting the valves V1-3 to obtain the correct flow rates through flow meters FM1-3. Manually adjusting the valves can be a tedious and time consuming process depending upon the method used to determine whether the valves are set correctly. The user may also tend to leave the valves where the valves are set rather than make small adjustments to the valves to optimize the process because it is usually time consuming to reset the valves. In a more automated system, a host computer monitors the output of the flow meters FM1-3 via an analog output signal such as 4-20 mA, or via a digital communications signal using a physical layer such as the CAN bus and a protocol such as DeviceNet. This type of setup requires the customer to develop and implement software to monitor the flow meters continuously, and to calculate the blend ratio and total flow rate. The user's software must also continuously adjust the valves to maintain the desired blend ratio and total flow rate via an electric or pneumatic control signal. Therefore, the user's software must spend a significant amount of time performing these low level monitoring, calculating, and adjusting tasks.
A flow device that addresses these and other shortcomings of known flow control and metering devices would be an important advance in the art.